Backlight unit

ABSTRACT

The present invention relates to a backlight unit that includes at least one first light emitting diode (LED) package and at least one second LED package, wherein the first LED package includes a blue LED chip, a green LED chip, and a first phosphor, the first phosphor being excited by blue light and to emit light to be mixed with blue light and green light respectively emitted from the blue LED chip and the green LED chip, the first LED package to thereby emit white light; the second LED package includes a blue LED chip, a red LED chip, and a second phosphor, the second phosphor being excited by blue light and to emit light to be mixed with blue light and red light respectively emitted from the blue LED chip and the red LED chip, the second LED package to thereby emit white light; and the first LED package and the second LED package are alternately arranged.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from and the benefit of Korean PatentApplication No. 10-2008-0030045, filed on Mar. 31, 2008, which is herebyincorporated by reference for all purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a backlight unit for providing a whitelight source in a liquid crystal display.

2. Discussion of the Background

A liquid crystal display (LCD) typically includes an LCD panel having athin film transistor (TFT) array substrate and a color filter substrate,which are opposite from and bonded to each other. The TFT arraysubstrate and the color filter substrate are spaced apart from eachother by a predetermined distance, and a liquid crystal layer isdisposed in the space between the substrates. The LCD also includes adriver for driving the LCD panel, and a backlight unit for supplyingbacklight to the LCD panel.

A conventional backlight unit emits white light that may be generated bya red-green-blue (RGB) full-color light emitting diode (LED) package orby a mixture of lights emitted from respective red, green, and blueLEDs. However, when the backlight unit is implemented using an RGBfull-color LED package or respective LED chips, there may be an unwantedincrease in manufacturing costs and decrease in yield.

SUMMARY OF THE INVENTION

The present invention relates to a backlight unit including at leastfirst and second light emitting diode packages.

Additional features of the invention will be set forth in thedescription which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention.

The present invention discloses a backlight unit that includes at leastone first LED package and at least one second LED package, wherein thefirst LED package includes a blue LED chip, a green LED chip, and afirst phosphor, the first phosphor being excited by blue light and toemit light to be mixed with blue light and the green light respectivelyemitted from the blue LED chip and the green LED chip, the first LEDpackage to thereby emit white light; the second LED package includes ablue LED chip, a red LED chip, and a second phosphor, the secondphosphor being excited by blue light and to emit light to be mixed withblue light and red light respectively emitted from the blue LED chip andthe red LED chip, the second LED package to thereby emit white light;and the first LED package and the second LED package are alternatelyarranged.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention, andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a view showing a backlight unit according to an exemplaryembodiment of the present invention.

FIG. 2 is a view showing a first LED package according to an exemplaryembodiment of the present invention.

FIG. 3 is a graph showing an optical spectrum of the first LED packageshown in FIG. 2.

FIG. 4 is a view showing a second LED package according to an exemplaryembodiment of the present invention.

FIG. 5 is a graph showing an optical spectrum of the second LED packageshown in FIG. 4.

FIG. 6 is a graph showing an optical spectrum of the backlight unitaccording to an exemplary embodiment of the present invention.

FIG. 7 is a graph showing an optical spectrum of a conventional RGBfull-color LED package.

FIG. 8 is a graph showing an optical spectrum of the backlight unitaccording to an exemplary embodiment of the present invention and anoptical spectrum of a backlight unit using the conventional RGBfull-color LED package.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The invention is described more fully hereinafter with reference to theaccompanying drawings, in which exemplary embodiments of the inventionare shown. This invention may, however, be embodied in many differentforms and should not be construed as limited to the exemplaryembodiments set forth herein. Rather, these exemplary embodiments areprovided so that this disclosure is thorough, and will fully convey thescope of the invention to those skilled in the art. In the drawings, thesize and relative sizes of layers and regions may be exaggerated forclarity. Like reference numerals in the drawings denote like elements.

It will be understood that when an element or layer is referred to asbeing “on” or “connected to” another element or layer, it can bedirectly on or directly connected to the other element or layer, orintervening elements or layers may be present. In contrast, when anelement is referred to as being “directly on” or “directly connected to”another element or layer, there are no intervening elements or layerspresent.

FIG. 1 is a view showing a backlight unit according to an exemplaryembodiment of the present invention.

Referring to FIG. 1, a backlight unit 10 according to the presentexemplary embodiment emits light by alternating current (AC) powersupplied from a power supply 20.

The backlight unit 10 comprises a plurality of LED packages 11 and 12.The LED packages 11 and 12 are disposed in two or more parallel lines.FIG. 1 shows backlight unit 10 having two parallel lines. The first andsecond lines are arranged such that their polarities are opposite toeach other.

Accordingly, when AC power is applied to the backlight unit 10 from thepower supply 20, current flows into the first line in a positive voltageregion during a positive phase of AC power so that the LED packagestherein emit light, while current flows into the second line in anegative voltage region during a negative phase of AC power so that theLED packages therein emit light.

Therefore, the first and second lines alternately emit light during acomplete phase of AC power, which includes one positive phase and onenegative phase of AC power. The first line having a positive voltageregion should emit light during the positive phase and not emit lightduring the negative phase, and the second line having a negative voltageregion should emit light during the negative phase and not emit lightduring the positive phase.

The LED packages 11 and 12 are alternately arranged in the backlightunit 10. The first LED package 11, which emits white light, includes ablue LED chip, a green LED chip, and a first phosphor. Light emittedfrom the first phosphor is mixed with blue and green lights respectivelyemitted from the blue and green LED chips to thereby emit white light.Although the first phosphor according to the present exemplaryembodiment is a red phosphor, the phosphor according to the presentinvention is not limited thereto. The second LED package 12, which emitswhite light, includes a blue LED chip, a red LED chip, and a secondphosphor. Light emitted from the second phosphor is mixed with blue andred lights respectively emitted from the blue and red LED chips tothereby emit white light. Although the second phosphor according to thepresent exemplary embodiment is a green phosphor, the phosphor accordingto the present invention is not limited thereto. Here, the blue lighthas a wavelength of 430 to 500 nm, the green light has a wavelength of500 to 580 nm, and the red light has a wavelength of 580 to 760 nm. Theblue light may have a wavelength of 450 to 470 nm, the green light mayhave a wavelength of 515 to 540 nm, and the red light may have awavelength of 620 to 640 nm.

Each of the first and second LED packages 11 and 12 includes LED chipson a substrate that are selected from blue, green, and red LED chipsthat emit light having at least different wavelengths. Each of the firstand second LED packages 11 and 12 also include a phosphor that isexcited by light emitted from at least one of the LED chips, performslight conversion, and allows light emitted from the phosphor to be mixedwith the lights emitted from the LED chips to thereby emit white light.

When AC current having a frequency of 60 Hz is applied to the first andsecond LED packages 11 and 12 of the backlight unit 10, each of the LEDpackages 11 and 12 is periodically turned on and emits light.

FIG. 2 is a view showing a first LED package according to an exemplaryembodiment of the present invention, and FIG. 3 is a graph showing anoptical spectrum of the first LED package shown in FIG. 2.

Referring to FIG. 2, the first LED package 11 includes a substrate 110and first and second electrodes 120 and 130 formed on the substrate 110.A first LED 150 emitting blue light is mounted on the first electrode120, and a phosphor 190, which is excited by the blue light and emitsred light having a peak wavelength longer than that of the excitationlight, is disposed over the first LED 150.

A second LED 160 is mounted on the second electrode 130 and emits greenlight having a different wavelength from that of the light emitted fromthe phosphor 190.

The first and second LEDs 150 and 160 may be electrically connected to athird electrode (not shown) through wires 1. However, the presentinvention is not limited thereto, and various alternate connectingmanners are possible.

A molding member 180 for encapsulating the first and second LEDs 150 and160 is formed on the substrate 110. The phosphor 190 for emitting redlight described above is contained in the molding member 180.

The substrate 110 may have a reflective portion (not shown) formed bymachining a predetermined recess in a central region of the substrate110 and allowing a sidewall of the recess to have a predetermined slope.

The first and second LEDs 150 and 160 may be mounted on a bottom surfaceof the reflective portion, so that the reflection of light emitted fromeach LED 150 and 160 can be maximized, thereby improving the lightemitting efficiency of the LED package 11.

The molding member 180 may be formed through an injection moldingprocess using a mixture of an epoxy or silicon resin and the phosphor190. Alternatively, the molding member 180 may be formed using aseparate mold and then pressurized or heat-treated. The molding member180 may be formed in various shapes including a convex lens shape, aflat plate shape, a shape having predetermined concavo-convex portionsformed on its surface, and the like.

The phosphor 190 contained in the molding member 180 for encapsulatingthe LEDs 150 and 160 formed on the substrate 110 may include at leastone of a silicate-based phosphor, a germanate-based phosphor, and agermanate-silicate-based phosphor.

The phosphor 190 may be uniformly distributed within the molding member180 as shown in FIG. 2. Accordingly, red light emitted from the phosphor190 may be mixed with blue and green lights respectively emitted fromthe first and second LEDs 150 and 160, to thereby emit white light. Inorder to improve color rendering, a phosphor (not shown) emitting yellowlight may be further contained in the molding member 180.

In the first LED package 11 according to the present exemplaryembodiment, blue light emitted from the first LED 150 excites thephosphor 190, which then emits light, and the second LED 160 emits lighthaving a different wavelength from the blue light and the light emittedby the phosphor 190, whereby the light emitted from the second LED 160is mixed with the light emitted by the first LED 150 and the phosphor190, and the first LED package 11 thereby emits light in a desiredspectrum region.

That is, blue and green lights are respectively emitted from the firstand second LEDs 150 and 160, and the phosphor 190 is excited by the bluelight and emits red light. Accordingly, the emitted lights having threewavelengths are mixed to thereby realize white light.

FIG. 4 is a view showing a second LED package according to an exemplaryembodiment of the present invention, and FIG. 5 is a graph showing anoptical spectrum of the second LED package shown in FIG. 4.

Referring to FIG. 4, the second LED package 12 includes a substrate 210and first and second electrodes 220 and 230 formed on the substrate 210.A first LED 250 emitting blue light is mounted on the first electrode220, and a phosphor 290, which is excited by the blue light and emitsgreen light having a peak wavelength longer than that of the excitationlight, is disposed over the first LED 250.

A second LED 260 is mounted on the second electrode 230 and emits redlight having a different wavelength from that of the light emitted fromthe phosphor 290.

The first and second LEDs 250 and 260 may be electrically connected to athird electrode (not shown) through wires 1.

A molding member 280 for encapsulating the first and second LEDs 250 and260 is formed on the substrate 210. The phosphor 290 for emitting greenlight described above is contained in the molding member 280.

The substrate 210 may have a reflective portion (not shown) formed bymachining a predetermined recess in a central region of the substrate210 and allowing a sidewall of the recess to have a predetermined slope.

The first and second LEDs 250 and 260 may be mounted on a bottom surfaceof the reflective portion, so that the reflection of light emitted fromeach LED 250 and 260 can be maximized, thereby improving the lightemitting efficiency of the LED package 11.

The molding member 280 may be formed through an injection moldingprocess using a mixture of an epoxy or silicon resin and the phosphor290. Alternatively, the molding member 280 may be formed using aseparate mold and then pressurized or heat-treated. The molding member280 may be formed in various shapes including a convex lens shape, aflat plate shape, a shape having predetermined concavo-convex portionsformed on its surface, and the like.

The phosphor 290 contained in the molding member 280 for encapsulatingthe LEDs 250 and 260 formed on the substrate 210 may include at leastone of a silicate-based phosphor, a germanate-based phosphor, and agermanate-silicate-based phosphor.

The phosphor 290 may be uniformly distributed within the molding member280 as shown in FIG. 4. Accordingly, green light emitted from thephosphor 290 may be mixed with blue and red lights respectively emittedfrom the first and second LEDs 250 and 260, to thereby emit white light.In order to improve color rendering, a phosphor (not shown) emittingyellow light may be further contained in the molding member 280.

In the second LED package 12 according to the present exemplaryembodiment, blue light emitted from the first LED 250 excites thephosphor 290, which then emits light, and the second LED 260 emits lighthaving a different wavelength from the blue and the light emitted by thephosphor 290, whereby the light emitted from the second LED 260 is mixedwith the light emitted by the first LED 250 and the phosphor 290, andthe second LED package 12 thereby emits light in a desired spectrumregion.

That is, blue and red lights are respectively emitted from the first andsecond LEDs 250 and 260, and the phosphor 290 is excited by the bluelight and emits green light. Accordingly, the emitted lights havingthree wavelengths are mixed to thereby realize white light.

FIG. 6 shows an optical spectrum of the backlight unit having the firstand second LED packages 11 and 12 arranged therein according to anexemplary embodiment of the present invention. Referring to FIG. 6, itcan be seen that the optical spectra of the first and second LEDpackages 11 and 12, respectively shown in FIG. 3 and FIG. 5, arecombined in the optical spectrum of the backlight unit.

FIG. 7 shows an optical spectrum of a conventional RGB full-color LEDpackage, and FIG. 8 shows an optical spectrum 1 of the backlight unitaccording to an exemplary embodiment of the present invention and anoptical spectrum 2 of a backlight unit using the conventional RGBfull-color LED package. A color reproduction range of the backlight unitusing the conventional RGB full-color LED package is maximally up to115%. On the other hand, a color reproduction range of the backlightunit according to an exemplary embodiment of the present invention ismaximally up to 94%. Accordingly, although the color reproduction rangeof the backlight unit according to an exemplary embodiment of thepresent invention may not equal that of the backlight unit using theconventional RGB full-color LED package, the backlight unit according tothe present invention can implement a backlight unit having a high colorreproduction range and a decreased manufacturing cost compared to theconventional RGB full-color LED package.

According to an exemplary embodiment of the present invention, abacklight unit is implemented by alternately arranging first LEDpackages, each of which comprises blue and green LED chips and a redphosphor to emit white light, and second LED packages each of whichcomprises blue and red LED chips and a green phosphor to emit whitelight, so that the backlight unit can substitute for a conventionalbacklight unit implemented using an RGB full-color LED package orrespective LED chips.

Further, according to an exemplary embodiment of the present invention,the number of LED chips used for the backlight unit is smaller than thatused for a conventional backlight unit implemented using an RGBfull-color LED package or respective LED chips, so that the probabilityof defects can be reduced to thereby improve yield and reliability.

It will be apparent to those skilled in the art that variousmodifications and variation can be made in the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A backlight unit, comprising: at least one first light emitting diode(LED) package and at least one second LED package, wherein the first LEDpackage comprises a blue LED chip, a green LED chip, and a firstphosphor, the first phosphor being excited by blue light to emit lightto be mixed with blue light and green light respectively emitted fromthe blue LED chip and the green LED chip, the first LED package tothereby emit white light; the second LED package comprises a blue LEDchip, a red LED chip, and a second phosphor, the second phosphor beingexcited by blue light to emit light to be mixed with blue light and redlight respectively emitted from the blue LED chip and the red LED chip,the second LED package to thereby emit white light; and the first LEDpackage and the second LED package are alternately arranged.
 2. Thebacklight unit of claim 1, wherein the first LED package and the secondLED package are disposed in a first line and a second line parallel withthe first line, and the first line and the second line have oppositepolarities.
 3. The backlight unit of claim 1, wherein the blue lightcomprises a wavelength of 430 to 500 nm, the green light comprises awavelength of 500 to 580 nm, and the red light comprises a wavelength of580 to 760 nm.
 4. The backlight unit of claim 3, wherein the blue lightcomprises a wavelength of 450 to 470 nm, the green light comprises awavelength of 515 to 540 nm, and the red light comprises a wavelength of620 to 640 nm.
 5. A backlight unit, comprising: a first set of lightemitting diode (LED) packages comprising first LED packages alternatelyarranged with second LED packages, wherein the first LED packagecomprises a first LED to emit a first light, a second LED to emit asecond light, and a first phosphor to emit a third light in response tothe first light, the first light, the second light, and the third lightbeing different colored lights that mix together to form white light,wherein the second LED package comprises a third LED to emit a fourthlight, a fourth LED to emit a fifth light, and a second phosphor to emita sixth light in response to the fourth light, the fourth light, and thefifth light, and the sixth light being different colored lights that mixtogether to form white light.
 6. The backlight unit of claim 5, furthercomprising: a second set of LED packages comprising first LED packagesalternately arranged with second LED packages; and a power source,wherein the first set of LED packages emit light in response to a firstphase of the power source, and the second set of LED packages emit lightin response to a second phase of the power source.
 7. The backlight unitof claim 6, wherein the first light is a blue light, the second light isgreen light, and the third light is a red light, wherein the fourthlight is a blue light, and the fifth light is a red light, and the sixthlight is a green light.
 8. The backlight unit of claim 7, wherein thefirst set of LED packages is arranged in a first line, and the secondset of LED packages is arranged in a second line that is parallel withthe first line.
 9. The backlight unit of claim 5, wherein the first LEDpackage further comprises a first molding member encapsulating the firstLED and the second LED, the first phosphor being contained within thefirst molding member.
 10. The backlight unit of claim 9, wherein thesecond LED package further comprises a second molding memberencapsulating the third LED and the fourth LED, the second phosphorbeing contained within the second molding member.